1. Field of the Invention
The present invention relates to a method and an apparatus for producing a solid product with a high purity using a reaction of gaseous raw materials with a plurality of components.
2. Description of Related Art
As a technique for producing a solid product using a reaction of gaseous raw materials with plurality of components, there is known a technique by which a metal with a high purity is produced by a gas phase reaction of a metal chloride gas and a reducing agent gas.
For example, there are disclosed a technique for producing ultrafine nickel powder by a gas phase reduction of a nickel chloride gas with a hydrogen gas (for example, see Patent documents 1 and 2) and a technique for producing nickel, copper or silver powder by a gas phase reduction of a nickel, copper or silver chloride gas with a hydrogen gas or a hydrogen sulfide gas (for example, see Patent document 3).
Further, there is indicated a technique of gas phase reduction of a gallium chloride gas with a vapor of zinc or other metals (for example, see Patent document 4), and furthermore, there is disclosed a method for producing polycrystalline silicon by a gas phase reduction of a silicon tetrachloride (SiCl4) gas with a metal reducing agent such as a zinc gas (for example, see Patent documents 5 and 6).
In particular, polycrystalline silicon with a high purity is used as a raw material of single-crystal silicon for semiconductors, and as a raw material of silicon for solar cells. In addition to the increase in demand for polycrystalline silicon for highly integrated semiconductors used in electronic devices and information technology devices, demand for polycrystalline silicon as silicon for solar cells has rapidly been expanded recently, but at this time, the supply capacity of polycrystalline silicon is short and there is a situation that the marketing needs cannot be met. Polycrystalline silicon is supplied preferentially to semiconductor usage, and accordingly polycrystalline silicon used as a raw material for production of solar cells must be used residues in a crucible after pulling up a single-crystal silicon for semiconductors and scraps such as cutting waste of single-crystal silicon ingot, so that polycrystalline silicon for solar cells is in a situation depending on the movement of semiconductor industry in terms of both quality and quantity, and always in short. It has been strongly desired to develop a technique for producing polycrystalline silicon as a raw material of silicon for solar cells in a larger amount and at lower cost than the existing technique.
Nowadays, the production of polycrystalline silicon conducted commercially has been carried out by a Siemens process, but this process has a high electric power consumption rate of manufacturing consumption rates and the operation of production devices is a batch type, so its production efficiency is low. Therefore, it is unsuitable as a production method in a large amount and at low cost.
In contrast, regarding a method for producing polycrystalline silicon using a gas phase reduction of a silicon tetrachloride (SiCl4) gas with a metal reducing agent such as a zinc gas, for example, silicon tetrachloride and zinc (Zn) gases are fed in a horizontal reactor made of quartz to grow polycrystalline silicon in the reactor. Therewith, zinc chloride (ZnCl2) as a by-product is separated into zinc and chlorine by a method such as electrolysis, and the obtained zinc is reused as a reducing agent and the obtained chlorine is used for the synthesis of silicon tetrachloride, thereby enabling the production of polycrystalline silicon in a large amount and at low cost in a recycling process.
However, in this technique of producing a solid product using a reaction of gaseous raw materials, there are problems that the resulting solid product is easily contaminated due to materials of a reactor, and also due to a by-product gas generated by the reaction and unreacted gaseous raw materials.    Patent document 1: JP H4-365806 A (1992)    Patent document 2: JP H8-246001 (1996)    Patent document 3: JP 2000-345218 A    Patent document 4: JP H1-25922 A (1989)    Patent document 5: JP 2003-34519 A    Patent document 6: JP 2003-342016 A
The present inventors have conducted many studies to solve pollution problems resulting from materials of a reactor in a method for producing polycrystalline silicon using a zinc gas as a reducing agent and a silicon tetrachloride gas as a raw material, and found that the problems are solved in such a way that a silicon chloride gas and a reducing agent gas are fed in a specific vertical reactor, polycrystalline silicon is generated at the tip of a silicon chloride gas feeding nozzle, and grown downward from the tip of the nozzle to prevent polycrystalline silicon from touching reactor walls. However, to further improve the quality, it is desired to establish a method for lowering an influence of a by-product gas generated by the reaction and unreacted gaseous raw materials as much as possible. Further, it is being desired to realize a method that allows polycrystalline silicon dropped in the lower part of a reactor to be continuously taken out of the reactor while maintaining the temperature of the reactor.